Apparatus for producing sound



1. BJ'O'RNST AD. APPARATUS FOR PRODUCiNG SOUND.

APPLICATION FILED SEPT. 8, 19!!!- 1,339,158. a Patented May 4,1920.

;JonGE1v 'B'JGRNSTAD, or READING, ENGLAND.

APPARATUS FOR PRODUCING SOUND.

Specification of Letters Patent.

Patented May 4, 1920.

Application filed. September 8, 1919. Serial No. 322,541.

To all whom it may concern:

Be it known that I, J oRoEN BJoRNsTAD, a subject of the King of Great Britain and Ireland, residing at Reading, in the county of Berks, England, have invented Improvements in Apparatus for Producing Sound, of which the following is a specification.

This invention relates to sound producing apparatus of the kind described in the specification of British Letters Patent No. 25268 of 1905, and known as a siren or diaphone, suitable for fog signaling and like purposes, in which the sound is produced by the action of fluid under pressure flowing through a slotted rotary piston that is reciprocated within a stationary slotted cylinder by the action of a fluid medium, and more particularly to apparatus of the kind referred to wherein the fluid medium used is steam.

In apparatus of this kind, the piston usually consists of two integrally connected portions,the larger of which, constituting the driving portion, is about double the area of the smaller or sound producing portion. In such apparatus it is essential to satisfactory working that an'eflicient cushion should be formed between the driving portion of the piston and the cylinder by the compression of the driving medium at the end of the outward stroke of the piston, so as to prevent metallic contact between the driving portion of the piston and the cylinder which would otherwise result in mechanical damage and ultimate breakdown.

The efficiency of this compression obviously depends on the one hand, on the provision of a sufliciently close fit between the soundprodu'cing portion of the piston and the corresponding portion of the cylinder'to prevent the leakage, between them, of the pressure medium and the consequent reduction in the efiiciency of the cushion. In order to insure prompt startingof the apparatus immediately upon admission of working fluid, it is, on the other hand, necessary that the piston should be quite free at the m'oment of starting.

Itis easy' to satisfy these somewhat conflicting conditions when working with compressed air, because the expanding air has the elfect of cooling the sounding portion of the piston, which is very thin. and light in comparison with the cylinder, so that the piston contracts in diameter to a slight ex tent and thereby increases the clearance between it and the cylinder at the moment of starting and before the cylinder has had time to be cooled to the same temperature, and when the piston has once got a good start, the subsequent reduction in clearance does not matter, because there is then ample driving power.

l Vhen however steam is used as the driving medium, the hot steam expands the sound-producing portion of the piston before the cylinder can expand to an equal extent, with the result that the clearance between the two is reduced and the piston is therefore liable to stick and fail to start .until the cylinder has had time to get heated to the same temperature, so as to restore the original clearance.

An attempt to obviate the diiiiculty merely by increasing the clearance between the piston and cylinder would result in impairing the efficiency of the compression cushion and bringing about metallic contact between the piston and cylinder with its resultant damage. Such increase of clearance is, however unavoidable, where prompt starting of the piston is necessary.

According to the present invention sufiicient clearance is provided between the piston and cylinder to permit of prompt starting and in order to maintain or restore the compression of the cushion, there is introduced between the sounding portion of the piston and the cylinder, a steam packing whereby leakageof steam from the compression or cushioning space is minimized or avoided.

To this end, according to one construction, the slits in the sounding portion of the piston are arranged at a greater distance from the driving portion of the piston than heretofore, so as to leave room for the formation -lIl the cylinder of one or more extra shts or holes which 1s or are formed in the cylinder opposite to a plain part of the sounding-portion of the piston, the arrangement being such as to keep the clearance space between the sounding portion of the piston and the cy linrtler'filled with a film of high pressure steam. Further to reduce the risk of leakage of steam, shallow grooves are or may be provided in the surface of the cylinder, or of the sounding portion of the piston, or in both surfaces, in proximity to the slit or slits, say, on each side of it or them.

instance the cylinder at, of the ordinary differential shape, is provided in its smaller portion with a circumferential slit 6, supplied with steam from the annular chamber 0, in the same way as are the sounding slits (Z in such smaller portion of the cylinder.

, A shallow circumferential groove '6 and two similar grooves e are formed in the inner surface of the cylinder at and arranged in relation to the slit 6, as shown, so as to re ceive steam therefrom and form a steam packing. Or, similar shallow grooves may be formed in the outer surface of the differential piston h, or in both of said surfaces, as shown, for the purpose mentioned.

With this arrangement, when steam. is compressed in the compression or cushioning space f above the larger and driving portion 9 of the differential piston, it will, under the circumstances described, then have opposed to it a back pressure in the clearance space between the smaller sounding portion h of the piston and the smaller portion of the cylinder a, equal, or nearly so, to its own pressure instead of that of the external atmosphere. As a result of this, there is a very considerable reduction in the leakage of steam from the said compression 'or cushionlng space 7 and consequent 1ncrease in the resultant pressure of compression and the elimination of metallic contact.

\Vhat I claim is 1'. Apparatus of the kind referred to, comprising a differential piston, a corresponding cylinder between which and the piston a cushioning space is provided and means whereby leakage of fluid from such space is prevented or reduced, for the purpose set forth.

2. Apparatus of the kind referred to, comprising a differential piston the larger portion of which serves as a driving member and the smaller portion as a sounding member, a differential cylinder for such piston, means whereby a portion of the driving fluid is imprisoned between the cylinder and piston to cushion the movement of the latter as it approaches the end of its stroke and means whereby another portion of the fluid is caused to serve as a packing for preventing or minimizing leakage of the cushioning fluid between the wall of the smaller cylinder portion and the companion sounding member of the piston.

8. In apparatus of the kind referred to, a differential cylinder the smaller portion of which is formed with a series of sounding slits extending to an annular surrounding steam space and with a circumferential slit between the sounding slits and the larger portion of the cylinder, one at least of the adjacent surfaces of the smaller portions of the piston and cylinderbeing formed with circumferential grooves adapted to receive steam from the said circumferential slit, for the purpose specified.

4. In apparatus of the kind referred to, a differential cylinder the smaller portion of which is formed witha series of sounding slits extending to an annular surrounding steam space, with a circumferential slit between the sounding slits and the larger portion of the cylinder and with a circumferentially grooved inner surface adapted'to receive steam from the said circumferential slit, for the purpose specified.

5. In apparatus of the kind referred to, a differential cylinder the smaller portion of which is formed with a series of sounding slits extending to an annular surrounding steam space, with a circumferential slit'between the sounding slits and the larger portion of the cylinder and with shallow circumferential grooves disposed upon the inner surface at opposite sides of the circum ferential slit aforesaid, for the purpose specified.

6. Apparatus of the kind referred to, comprising a differential cylinder the smaller portion of which is formed with a' series of sounding slits surrounded by an annular steam chamber,,a differential piston having a sounding portion occupying the smaller cylinder portion and a driving portion adapted to work in the larger cylinder portion, means whereby a portion ofthe steam is periodically imprisoned between the driv- JoReEN BJoRNsTAD. 

